Naked Black Holes Would Shock the Foundations of Relativity

Researchers from Duke University and the University of Cambridge are investigating stars that can collapse and compress into what Albert Einstein termed singularities, or black holes, which are entities so confining and massively dense that light can never escape beyond their "event horizons."

The question Arlie Petters, a Duke professor of mathematics and physics, and astrophysics Ph. D. candidate Marcus Werner of Cambridge University are asking is whether naked singularities could exist in certain instances. Naked singularities are black holes which do permit light to escape the event barrier in certain kinds of situations.

Albert Einstein theorized that stars bigger than the sun can collapse and compress into singularities that we call black holes. These entities are so confining and massively dense that the laws of physics break down inside them: light cannot break free from their gravity and therefore cannot be seen as visible light.

The theory explaining the phenomenon of confined light is the "cosmic censorship conjecture." This conjecture says that in realistic nature a barrier, the event barrier, surrounds singularities preventing light from escaping. Thus they appear perpetually black to the rest of the universe. The conjecture of cosmic censorship is very difficult to prove, and very difficult to disprove, according to Petters.

Kip Thorne and John Preskill, two experts in the cosmology of relativity at the California Institute of Technology, have suggested for more than a decade that naked singularities--those with light not confined behind an event barrier in accord with the cosmic censorship conjecture--could exist in certain instances

Because the obscuring outward matter surrounding singularities has never been fully penetrated, astronomers cannot say for sure whether all black holes are actually black, retaining light behind and event barrier, Petters said. Scientists can only point to effects of emissions of highly energetic radiation or the extreme orbits of nearby stars, both of which are effects caused by the massive gravitational pull of certain unseen entities on the matter surrounding them.

Arlie Petters and Marcus Werner think that there is a way to determine whether some black holes are actually naked. Finding such an unmasked, naked form of a singularity "would shock the foundation of general relativity," according to Petters.

Petters and Werner used previous work that indicates that gravitational lensing--massive gravity splitting light into multiple images--can show whether cosmic censorship can ever be violated for non-spinning singularities (black holes). However, suspected singularities discovered by astronomers all appear to be rapidly spinning, sometimes at more than 1,000 times a second.

Employing another finding that a covered black hole can become a naked black hole if its angular momentum, which is caused by its spin, is greater than its mass, Petters and Werner calculated in six equations that an uncovered, naked singularity's massive gravitational pull would split the light of stars or galaxies in the background behind it--from the perspective of an observing telescope--in specific and "telltale" ways that are potentially detectable by astronomers using existing or soon-to-be instruments.

"If you ask me whether I believe that naked singularities exist, I will tell you that I'm sitting on the fence," said Petters. "In a sense, I hope they are not there. I would prefer to have covered-up black holes. But I'm still open-minded enough to entertain the 'otherwise' possibility."

Werner and Petters first began interacting in the Duke professor's native Belize, where Petters has established an institute for math and science education and the Cambridge graduate student had come to help excavate a Mayan ruin.

The report was posted online for the research journal Physical Review D.

Monte Basgall, "Collaboration shines possible light on objects 'weirder than black holes'," Duke University.